During neurosurgical procedures, electrodes are commonly used to monitor electrical activity and stimulate and/or lesion neural tissue. Typically, electrodes are brought into the vicinity of cell membranes so that an electrical transition resistance (impedance) is created between the cells and the electrodes. Electrical stimulation of a malfunctioning neuron can be used to activate or reversibly block neural activity, while lesioning can be used to permanently disable neuronal activity. U.S. Pat. No. 1,662,446, issued to Wappler, teaches an early electrode system.
The recent resurgence of procedures to stimulate and produce lesions in deep brain structures for the treatment of Parkinson's disease, tremor, and dystonia, has been due not only to a better understanding of functional neuroanatomy of the cells involved in these diseases (Albin et al., 1995, Trends in NeuroScience 18(2): 63–4; Alexander et al., 1990, Prog. in Brain Res. 85: 119–46) but also to the development of techniques for accurately localizing these cells (Lang et al., N. Engl. J. Med. 339(16): 1130–43). Microelectrode recording allows direct recording and characterization of the activity of neural cells and can be used to record individual cells at a spatial interval from a micron to 100 microns and in a frequency range from 1 Hz to 200 Hz (see, e.g., Albe-Fessard et al., 1963, Ann. Chir. 17:1185–1214; Albe-Fessard et al., 1963, Electroencephalogr. Clin. Neurophysiol. 15: 1052; Jasper et al., 1963, Physiologist 7: 167).
While microelectrodes provide the best means of localizing diseased cells, generally, microelectrodes must be inserted into the brain multiple times (e.g., at target sites separated by about 2 mm) to sufficiently characterize the physiology of a region which is to be stimulated or lesioned. Probes comprising groups of microelectrodes bundled together at high density (“multichannel microelectrodes”) increase the resolution of individual recording passes, and can stimulate and record a 20–200 μm radius around an insertion site (see, e.g., Gross et al., 1999, Brain 122(Pt3): 405–16; Gross et al., 1999, J. Neurosurg. 90(3): 468–77; Ranck, 197, Brain Res. 98: 417–440). Typically, a multichannel microelectrode is inserted at a location, and when a site of pathology is identified, it is removed and replaced by a larger diameter macroelectrode (e.g., about 1.1 mm) which is used to validate target location and for subsequent stimulating and/or lesioning as appropriate. However, even multichannel microelectrodes must be inserted and removed at least three to five times to obtain good target localization and macroelectrodes generally must be inserted separately.
Multichannel electrodes which combine the recording functions of microelectrodes and the stimulating functions of macroelectrodes have been reported. Generally, these systems consist of recording and stimulating wires which radiate from a planar backbone (see, e.g., U.S. Pat. No. 5,282,468). Because of the large surface area these electrodes occupy, they generally are suited only for recording and stimulating neurons at the surface of the brain and are not for use in deep brain procedures.